Method of forming and the resulting membrane composition for surgical site preservation

ABSTRACT

A method of forming and the resulting membrane composition for securement to a patient&#39;s bone or tissue to reduce the formation of tissue adhesions following a surgical procedure comprises a first component and a second component. The first component comprises a hydrogel including at least one crosslinked polymer. The second component comprises a textile component. The composition has a thickness between about two tenths of a millimeter (0.2 mm) to about six tenths of a millimeter (0.6 mm), a suture retention strength between about one Newton (1 N) to about thirteen Newtons (13 N), a static coefficient of friction between about one hundredth (0.01) and about one-half (0.5), a kinetic coefficient of friction between about one hundredth (0.01) and about one-half (0.5) and a flexibility of less than thirty millimeters (30 mm) bend length. A method of reducing the occurrence of tissue adhesions following surgery comprises applying the membrane composition to a surgical site.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 13/142,294 filed on Jun. 27, 2011, which is a national stageentry pursuant to 35 U.S.C. §371 of International Patent Application No.PCT/US2008/088444 filed on Dec. 29, 2008. These references are herebyincorporated by reference herein in their entireties.

FIELD OF THE INVENTION

The present invention relates to a method of forming, and the resultingmembrane composition that functions as a barrier to preserve a surgicalsite and/or plane and minimize bodily tissue adhesions that may formafter medical procedures.

BACKGROUND OF THE INVENTION

In surgical procedures, the steps involved in dissection, cauterization,suturing, etc. cause trauma to surrounding tissue and initiate theformation of local post surgical adhesions.

After surgical procedures such as anterior access spine surgery, generalabdominal and pelvic surgery, cardiothoracic surgery, etc., a woundrepair process begins in which scar tissue is laid down that disruptsthe normal anatomic planes and results in soft tissue adhesions. Theseadhesions can cause post operative pain, bowel obstructions, and othercomplications. Further, upon revision surgery this scar tissue can causea nearly blind navigation field and present challenges with mobilizationof scarred down tissues (i.e., tissues that have adhered to nearby softtissues, bone tissues or surgical implants). Vessel damage, nervedamage, and other soft tissue injury can be a hazard upon revisionsurgery.

After trauma surgery adhesions can form at the fracture site due to bonespurs or by attachments to the titanium or stainless steel plates orscrews. These adhesions with surrounding tissues can causepost-operative complications such as tendon irritations, loss of tendonmobilization, and impaired local joint function. Further, theseadhesions can cause challenges (and may result in surgicalcomplications) during a subsequent hardware removal procedure.

In anterior access spine surgery, such as total disc arthroplasty,anterior lumbar interbody fusion and anterior plating, the soft tissueand blood vessels in front of the spine are mobilized during the accessportion of the surgery. After the procedure, these vessels typicallyscar down (i.e., adhere) to the surgical site. These adhesions of thevessels increase the risk of vascular injury if a revision procedureneeds to be performed. The incidence of vascular injury on revisionsurgical cases has been reported to be as high as fifty-seven percent(57%). A barrier device in these applications would serve two functions,first as a covering to protect the vessels from the hardware used in thespinal procedure and second as a guide and plane of dissection duringthe revision procedures to help remobilize the vessels.

In other spine applications a barrier can be useful as well. Forexample, in scoliosis treatment with growing rod procedures, it may beuseful to prevent the growth of tissue onto the screws that will need tobe accessed during the subsequent lengthening procedures. In cervicalprocedures a barrier could prevent adhesions from the esophagus to thespinal implants and surgical site in order to prevent complications suchas dysphasia, irritations and erosion of the esophagus. In posteriorspinal procedures, a barrier device can function as a dura repair orhelp to limit nerve root tethering post discectomy.

In cardiothoracic surgery, a barrier device can function to helpfacilitate re-operations for cardiac patients, by minimizing adhesionformations between the sternum and other tissues.

Similar challenges with adhesions have been described in generalabdominal pelvic surgery as well as other surgical treatments.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to a method of forming and the resultingmembrane composition that functions as a barrier to preserve thesurgical site and/or plane and prevent surgically induced adhesions.

One embodiment of the present invention may comprise a membranecomposition for securement to a patient's bone or soft tissue to reducethe formation of tissue adhesions following a surgical procedurecomprising a first component and a second component. The first componentcomprises a hydrogel including at least one crosslinked polymer. Thesecond component comprises a textile component, wherein the membranecomposition has a thickness between about two tenths of a millimeter(0.2 mm) to about six tenths of a millimeter (0.6 mm), a sutureretention strength between about one Newton (1 N) to about thirteenNewtons (13 N), a static coefficient of friction between about oneone-hundredth (0.01) and about one-half (0.5), a kinetic coefficient offriction between about one one-hundredth (0.01) and about one-half (0.5)and a flexibility of less than thirty millimeters (30 mm) bend length.

Another embodiment of the present invention may comprise a membranecomposition for securement to a patient's bone or tissue comprising afirst component and a second component. The first component comprises ahydrogel including at least one polymer selected from the groupconsisting of poly(vinyl alcohol), poly(vinyl pyrrolidone),poly(hydroxyethylmethacrylate), poly(acrylamide), poly(acrylic acid),poly(acrylonitrile), polyethylene imine and poly(ethylene glycol),wherein the at least one polymer is crosslinked. The second componentcomprises a textile component. The composition has sufficient thickness,suture retention strength, friction coefficient and flexibility toreduce the formation of tissue adhesions following a surgical procedure.

A further embodiment of the present invention may comprise a membranefor use as a surgical implant comprising a first component and a secondcomponent. The first component comprises a hydrogel including at leasttwo polymers selected from the group consisting of poly(vinyl alcohol),poly(vinyl pyrrolidone), poly(hydroxyethylmethacrylate),poly(acrylamide), poly(acrylic acid), poly(acrylonitrile), polyethyleneimine and poly(ethylene glycol), and the second component is selectedfrom the group consisting of polypropylene, polyester,polyetheretherketone and expanded polytetrafluoroethylene. The textilecomponent is formed of fibers having a thickness from about twohundredths of a millimeter (0.02 mm) to about three millimeters (3.00mm). The fibers form pores from about fifteen thousandths of amillimeter (0.015 mm) to about twelve and seven tenths millimeters (12.7mm) in size and the textile component is encapsulated by the firstcomponent. The membrane has a thickness between about two tenths of amillimeter (0.2 mm) and about six tenths of a millimeter (0.6 mm).

A further embodiment of the present invention may comprise a method ofreducing the occurrence of tissue adhesions following surgery comprisingapplying a membrane composition comprising a first component and asecond component, wherein the first component comprises a hydrogelincluding at least one crosslinked polymer, the second componentcomprises a textile component, wherein the composition has a thicknessbetween about two tenths of a millimeter (0.2 mm) to about six tenths ofa millimeter (0.6 mm), a suture retention strength between about oneNewton (1 N) to about thirteen Newtons (13 N), a water content betweenabout fifty percent (50%) and about eighty percent (80%) and aflexibility of less than thirty millimeters (30 mm) bend length to apatient's bone or tissue.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofthe preferred embodiments of the application, will be better understoodwhen read in conjunction with the appended drawings. The drawings,examples and embodiments described within this specification are to beunderstood as illustrative and exemplary of structures, features andaspects of the present invention and not as limiting the scope of theinvention. It should be understood that the application is not limitedto the precise arrangements and instrumentalities shown. In thedrawings:

FIG. 1A shows a top plan view of a first preferred embodiment of aportion of a membrane composition of the present invention held in placeby a suture;

FIG. 1B shows a magnified top plan view of a textile component of themembrane composition shown in FIG. 1A;

FIG. 1C shows a cross-sectional view of the membrane composition of FIG.1A;

FIG. 2 is a graphical representation of a friction force test of anexample of the membrane composition of FIG. 1A;

FIG. 3 is a graphical representation of the suture strength of anexample of the membrane composition of FIG. 1A;

FIG. 4 is a graphical representation of the tensile strength of anexample of the membrane composition of FIG. 1A;

FIG. 5 is a graphical representation of the bending rigidity of anexample of the membrane composition of FIG. 1A;

FIGS. 6A and 6B are histological sections of rat tissue containing anexample of the membrane composition of FIG. 1A;

FIG. 7A is a FT-IR spectrum analysis of a pre-conditioned an example ofthe membrane composition of FIG. 1A; and

FIG. 7B is a FT-IR spectrum analysis of a post-conditioned an example ofthe membrane composition of FIG. 1A.

DETAILED DESCRIPTION OF THE INVENTION

The methods, examples and embodiments described within thisspecification are to be understood as illustrative and exemplary ofstructures, features and aspects of the present invention and not aslimiting the scope of the invention. Certain terminology is used in thefollowing description for convenience only and is not limiting. Thewords “right”, “left”, “top” and “bottom” designate directions in thedrawings to which reference is made. The words “inwardly” and“outwardly” refer to directions toward and away from, respectively, thegeometric center of the device and designated parts thereof. The words,“anterior”, “posterior”, “superior”, “inferior”, “lateral” and relatedwords and/or phrases designate preferred positions and orientations inthe human body to which reference is made and are not meant to belimiting. The terminology includes the above-listed words, derivativesthereof and words of similar import.

A thin membrane to act as a barrier to preserve a tissue site and/orplane between implanted surgical devices and surrounding tissue orbetween apposing tissues that may form together after surgeries causingcomplications would be desirable and useful. It is further desired thatthe barrier be made of a biocompatible and stable material that has theappropriate material and mechanical properties to help facilitateplacement. A strong, flexible, and thin material is preferred that canconform and drape over plates or be contoured to specific patientanatomy while still having sufficient strength to allow for fixation andto remain in place throughout the healing process. It is also desirablethat the barrier exhibit sufficient lubricity to inhibit tissue adhesionformation while also having sufficient “stickiness” to allow for ease ofplacement during a surgical procedure.

It is also desirable that the barrier be formed of a compliantnon-absorbable sheet like material with low porosity to prevent tissuein-growth or cellular penetration. It is preferred that the barrier beformed of a permanent and nonabsorbable thin material that will remainstable and not decompose after a length of time in a patient to therebyfacilitate a potential revision procedure by providing a plane ofdissection. Finally, it will be desirable that the barrier provide anavigation function during revision surgeries by the inclusion ofseparate and distinct markings with the option to make such markingsradiopaque.

One embodiment of the barrier may comprise a membrane composition 5comprising a first component 10 and a second component 20, wherein thefirst component 10 comprises a hydrogel including at least onecrosslinked polymer and the second component 20 comprises a textilecomponent, a base substrate or a filler biomaterial. The first component10, also referred to as the matrix in this example, may be a hydrogelcomponent that may be either chemically crosslinked to the basesubstrate, such as, for example, a filler or a mesh, or physicallyintertwined with the base substrate during the manufacturing process.The base substrate may be created from common surgical textiles that areeither woven, knit, or braided. Various materials may function as thebase substrate such as, for example, common surgical textile materialssuch as, but not limited to, polyester, expanded polytetrafluoroethylene(ePTFE), polyetheretherketone (PEEK), polyethylene (PE), andpolypropylene (PP). The hydrogel component may provide the membranecomposition with its lubricious characteristics. The textile componentmay provide increased strength to allow the membrane component to beattached to soft tissue, bone tissue or a surgical implant. Theincreased strength of the membrane composition also allows it to bear aload such as, for example, compression from an adjacent organ in apatient. FIG. 1A shows a preferred membrane composition 5 of the presentinvention held in place by a suture 2. The first component 10,encapsulates the second component 20. FIG. 1B shows an exemplary textilecomponent of a membrane composition having courses 22, wales 24 andpores 25. FIG. 1C shows a cross-section of a membrane composition havinga thickness t.

One embodiment of the present invention may comprise a membranecomposition 5 comprising a first component 10 comprising a hydrogelincluding at least one crosslinked polymer, including, but not limitedto, poly(vinyl alcohol) (PVA), poly(vinyl pyrollidone) (PVP),poly(hydroxyethylmethacrylate) (pHEMA), poly(acrylamide) (PAm),poly(acrylic acid) (PAA), poly(acrylonitrile) (PAN), polyethylene imine(PEI) or poly(ethylene glycol) (PEG). The hydrogel component 10 may havepolymer concentrations ranging from about five percent (5%) to aboutsixty percent (60%) prior to combining with the base substrate,preferably about eight percent (8%) to about thirty-two percent (32%),more preferably about eleven and one-half percent (11.5%) to abouttwenty percent (20%). The creation of a spinal implant comprised of aPVA-based hydrogel is disclosed in U.S. Pat. No. 7,214,245, which isincorporated herein by reference.

Another embodiment of the present invention may comprise a membrane 5composition comprising a first component 10 comprising a PVA-basedhydrogel, wherein the PVA may be crosslinked to a second polymerincluding, but not limited to, PVP, pHEMA, PAm, PAA, PAN, PEI or PEG.The ratio of PVA to second polymer may range from about 1:1 to about200:1, preferably about 5:1 to about 150:1, more preferably about 75:1to about 110:1.

A further embodiment of the present invention may comprise a membranecomposition 5 comprising a second component 20 which may comprise atextile component. The textile component 20 may be based on a surgicaltextile. Surgical textiles may be made from a variety of monofilament ormultifilament materials such as, for example, but not limited to,polypropylene, polyester, PEEK, ePTFE or other permanent textilematerials. The textile component may be mesh or felt or other constructsand made in a variety of manners such as, but not limited to, braiding,knitting, or weaving. The textile component 20 may have a linear densityfrom about thirty (30) denier to about three hundred (300) denier. Theknit versions may have courses 22 per inch ranging from about two (2) toabout two hundred (200) courses per inch, preferably between about forty(40) to about one hundred ten (110) courses per inch and more preferablybetween about sixty (60) to about eighty (80) courses per inch. The knitversions may have wales 24 per inch values ranging from about two (2) toabout one hundred (100) wales per inch, preferably between abouttwenty-five (25) to about sixty (60) wales per inch, more preferablythirty-six (36) to about forty-five (45) wales per inch. The thicknessof the textile component or base substrate may range from about twohundredths of a millimeter (0.02 mm) to about three millimeters (3.00mm), preferably between about nine hundredths of a millimeter (0.09 mm)to about one and two tenths millimeters (1.2 mm), more preferably aboutone tenth of a millimeter (0.1 mm) to about two tenths of a millimeter(0.2 mm). The pores 25 in the textile component may range from aboutfifteen thousandths of a millimeter (0.015 mm) to about twelve and seventenths millimeters (12.7 mm) in order to provide an interlocking withthe gel matrix. Preferably the pores in the textile component range fromabout five hundredths of a millimeter (0.05 mm) to about five and seventenths millimeters (5.7 mm), more preferably two tenths of a millimeter(0.2 mm) to about three tenths of a millimeter (0.3 mm).

Another embodiment of the present invention may comprise a membranecomposition capable of being stored in a variety of media such as, forexample, but not limited to, phosphate buffered saline (PBS) solutions,aqueous polymer solutions, aqueous ionic solutions, pH specifiedsolutions, antimicrobial solutions, or protein-containing solutions fordrug delivery applications.

Another embodiment of the invention may comprise a method for formingthe membrane composition 5. The hydrogel component 10 may be first madeinto a solution and then applied, rolled, or molded with the textilecomponent 20. The at least one polymer of the hydrogel component 10 maybe crosslinked in a variety of manners. The hydrogel component 10 may bemolded and then chemically crosslinked by radiation or chemical means.The hydrogel component 10 may be only physically crosslinked in avariety of manners such as, for example, but not limited to,cryogelation (i.e., freezing and thawing), dehydration processing, or bymixing of the components in the manner of Theta gels (i.e., preparationof a stable gel formulation by competitively removing excess solvent(e.g., water) using a further component which has a higher affinity forthe solvent than the hydrogel component). A combination of any of thecrosslinking methods may be combined in which the hydrogel component 10is first physically crosslinked and then chemically crosslinked, suchas, for example, by electron beam ultra violet or visible radiation orgamma irradiation. After or during the crosslinking methods the hydrogelcomponent 10 may be packed in a sterile barrier system with anappropriate storage media.

The embodiments of the present invention preferably provide superiorsurgical handling properties when compared to standard surgicalmembranes that are often too weak for adequate fixation or have “SaranWrap” like qualities that make placement a challenge. The preferredmembrane composition 5 of the present invention may be made very thinyet provide sufficient strength to allow for suture or tack fixation.Suture strength is valuable in order to reliably fasten the membranecomposition to soft tissue or bone during a surgical procedure.Preferred membrane compositions 5 of the present invention may have asuture retention strength ranging from about one Newton (1 N) to aboutthirteen Newtons (13 N), preferably from about four Newtons (4 N) toabout nine Newtons (9 N), more preferably from about six Newtons (6 N)to about seven Newtons (7 N).

In addition, the membrane composition 5 of the preferred embodiment maybe made to be very flexible so that the barrier may contour or drapeover plates or anatomical structures without or by minimizing wrinklingor bubbling of the membrane composition 5. It is preferred that theflexibility of the membrane composition 5 of the present invention beless than thirty millimeters (30 mm) bend length and less than 10 grammillimeters (10 g·mm) bending rigidity. Further, the surface of themembrane composition 5 may be a hydrogel that emits surface waterthroughout the surface of the membrane composition 5 in order to actwith a slight surface tension (i.e., for example, to provide similar orequivalent surface energy to that of natural tissues to provide orpromote a slight surface tension) allowing the product to temporarilystick to tissue and metal during procedural placement. This surfacetension effect helps with arrangement of the barrier and because the gelis hydrophilic, and thus carrying its own surface water, this effectalso occurs on dry surfaces such as, for example, surgical retractors,plates, pedicle screws, spinal rods, etc. The preferred membranecomposition 5 of the present invention may also be sufficientlytransparent to assist in identification of structures beneath themembrane composition 5 during placement. Additionally, the membranecomposition 5 may be stretchable and mimic soft tissue characteristicsby establishing, for example, large strains under small loads thatallows the flexible material to further contour and bend withsurrounding soft tissue structures during and/or after placement.

The preferred membrane composition 5 of the present invention may bebiocompatible and have long term stability in vivo. The preferredmembrane composition 5 of the present invention may provide for a lowporosity surface that limits tissue in-growth and cellular penetration.The membrane composition of the present invention may also comprise acoating which may be drug-eluting. The drug-eluting coating may elutecompositions such as, for example, drug compositions, antibodies orhormones.

Further, the preferred membrane composition 5 of the present inventionmay provide for a barrier material with lubricious and low frictionsurfaces to prevent apposing tissue erosion over long term use. Thestatic coefficient of friction of the preferred membrane compositions 5may be, for example, about one hundredth (0.01) to about one-half (0.5),preferably about four hundredths (0.04) to about twenty-four hundredths(0.24), more preferably about six hundredths (0.06) to about eighteenhundredths (0.18). The kinetic coefficient of friction of the preferredmembrane compositions 5 may be, for example, about one hundredth (0.01)to about one-half (0.5), preferably about four hundredths (0.04) toabout twenty-four hundredths (0.24), more preferably about sixhundredths (0.06) to about eighteen hundredths (0.18).

In addition, the preferred membrane composition 5 of the presentinvention may provide for the addition of radiopaque or other colormarkings within the material to provide a navigation function duringre-operations. The membrane composition 5 of the preferred embodiment ofthe present invention may provide for a covering of sensitive anatomicstructures, maintenance of surgical site and/or tissue planes during thehealing process and a navigation function during revision surgeries,both by its ability to be used as a plane of dissection and by itsability to be identified through pre-operative x-ray type methods.

The preferred membrane composition 5 of the present invention may haveexcellent handling properties. Improved handling is desirable for anysurgical device but, with a thin and flexible membrane composition 5 ofthe preferred embodiment, it is preferred that the membrane composition5 be capable of being laid in place properly and be fastenable to thesurrounding structures. The membrane composition 5 of the preferredembodiment of the present invention provides for a thin membrane that ishighly flexible and can contour to surfaces preferably without orminimizing bubbling or wrinkling. Further the membrane composition 5 ofthe preferred embodiment of the present invention may be made thin whilemaintaining sufficient strength required for fixation due to thecombination of filler material or base substrate and gel strength. Inaddition, the preferred membrane composition 5 of the present inventionmay have the ability to stretch during placement without creating ahighly tensioned construct that could tear after placement.

Embodiments of the present invention may be made semi-transparentallowing the surgeon to visualize structures below the membranecomposition 5 during placement.

Membrane compositions 5 of the preferred embodiment of the presentinvention may have a surface water content that allows for surfacetension effects to facilitate ease of flattening and placement prior tofixation. Once sealed in the body this surface water provides alubricious and low friction surface to the surrounding tissues thuspreventing potential complications such as tissue erosion or tissueadhesions. The preferred water content of the membrane composition 5 maybe between about fifty percent (50%) and about eighty-five percent(85%), more preferably between about sixty percent (60%) to about eightypercent (80%), more preferably between about sixty-eight percent (68%)to about seventy-five percent (75%). Within this range, the membranecomposition 5 has preferred handling characteristics. Lower watercontent generally leads to stiffer handling and will not contour aseasily.

A further embodiment of the present invention may comprise a method ofmanufacture of the membrane compositions 5 that provides for inking ormarking of the textile component 20 in any desired location to assistwith the surgical procedure. The ink may be non-radiopaque and used asmarkers during placement or used as a method to identify the barrierduring a re-operation by making the membrane composition 5 a distinctcolor from the surrounding tissue. Further, the ink may be maderadiopaque to allow for specific markings to be included that can helpplan a re-operation and locate the membrane composition 5. Additionally,metallic grommets, clips, eyelets or the like may be affixed to thetextile component 20 to provide radiopaque marking or a predeterminedpoint of fixation.

The embodiments of the present invention preferably are hydrophilic andsynthetic. The membrane compositions 5 of the preferred embodiment ofthe present invention may be gamma sterilizable and non-absorbable. Thepreferred membrane compositions 5 of the present invention may have asufficiently low porosity to prevent tissue in-growth and cellularinfiltration, but still allow for the transport of small moleculesthrough the membrane composition 5.

The preferred embodiments of the present invention may be made withoutany toxic crosslinking agents which provides for a very inert biologicreaction while the membrane composition 5 is implanted in a patient.Further, the preferred membrane compositions 5 of the present inventionmay be nonabsorbable, permanent, and stable within the body. Themembrane compositions 5 of the preferred embodiment of the presentinvention may be sufficiently flexible to allow for contouring without,or by minimizing, bubbling or wrinkling, thereby providing for smoothplacement and can potentially prevent areas or vacuums that can be sitesfor post-surgical infections.

The preferred embodiments of the present invention may exhibitmechanical properties that contribute to optimum surgical performance.For instance, the membrane composition 5 may be thin and, therefore,unobtrusive to the surrounding anatomy. Even though it may be thin, themembrane composition structure may be sufficiently strong to allow forfixation of the membrane composition 5. The membrane composition 5 mayhave a thickness range, for example, from about two tenths of amillimeter (0.2 mm) to about three millimeters (3 mm), preferably fromabout three tenths of a millimeter (0.3 mm) to about one and one-halfmillimeters (1.5 mm), more preferably from about three tenths of amillimeter (0.3 mm) to about nine tenths of a millimeter (0.9 mm).Thicker membrane compositions 5 could compress vessels or soft tissue.In applications near the esophagus, such configurations could causedysphasia.

The membrane composition 5 and manufacture of the preferred membranecomposition 5 may be modified in different manners to provide formechanical properties similar to soft tissue located anywhere in thebody. In other words, the membrane composition 5 can be tailored tospecific performance requirements or preferred characteristics needed inthe chosen area of the body. The membrane composition 5 may be resistantto breakdown or delamination. The exposed gel surface of the preferredmembrane composition 5 may have sufficiently low friction and besufficiently lubricious to provide for interaction with adjacentsensitive anatomical structures without causing any tissue erosion ortissue adhesions.

EXAMPLES AND EXPERIMENTS

The following examples and experiments describe some of the propertiesof the preferred membrane compositions 5 described herein and are onlyintended to assist in explaining and illustrating certain structures,features and aspects of the membrane composition and not as limiting thescope of the invention to the precise arrangements, compositions,properties or features described.

Example 1 Membrane Composition Formulation and Characterization

A preferred membrane composition 5 comprising a PVA-based hydrogelcomponent 10 with a porous mesh filler component 20 was prepared. Themesh 20 consisted of a fifteen hundredths of a millimeter (0.15 mm)thick knit polyester fabric with medical grade radiopaque ink markings.The PVA-based hydrogel component 10, as described in more detail below,was applied to completely cover the mesh and form the membranecomposition 5.

The hydrogel component 10 was created by preparing a twelve and eighttenths percent (12.8%) aqueous polymer solution of PVA and PVP at a 99:1ratio. At an elevated temperature of approximately eighty degreesCelsius (80° C.), the warm polymer solution was transferred onto thepolyester mesh with ink and then drawn over the mesh to form a uniformlayer on both sides. The final preferred membrane composition 5 wasapproximately three tenths of a millimeter (0.3 mm) thick. A process ofcyrogelation (i.e., freezing and thawing) was used to create physicalcrosslinks in the hydrogel component 10. The mesh 20 and ink wereencapsulated by the hydrogel component 10 on all sides resulting in acontinuous permanent PVA-based hydrogel component. The membranecomposition 5 was then packed in a tray with a PBS solution andsubjected to gamma sterilization, which further chemically crosslinkedthe hydrogel component 10. Compositional analysis was performed on themembrane composition 5.

The water content of this preferred membrane composition 5 wasdetermined according to the “Loss on Drying” method as described in theGravimetric Method from the 2003 United States Pharmacopoeia/NationalFormulary (USP/NF). Briefly, the membrane composition 5 was heated toone hundred five degrees Celsius (105° C.) to evaporate any watercontained in the hydrogel component 10. The mean water content of thirty(30) hydrogel compositions was determined to be seventy-five and threetenths percent (75.3%)±one and eight tenths percent (1.8%).

A mass balance calculation of a one hundred gram (100 g) sample wasperformed. Table 1 displays the mass of each component.

TABLE 1 Composition analysis of 100 g Sample Total PVA PVP PolyesterWater 100 g Sample 10.9 g 0.1 g 13.7 g 75.3 g 100 g

The thickness of the membrane composition 5 was measured using a tenounce (10 oz.) constant load thickness gage according to the methoddescribed in “ISO 5084 Determination of Thickness of Textiles andTextile Products” method. A twenty-eight and seven tenths millimeters(28.7 mm) diameter platen was lowered on the test samples. The meanthickness of the thirty hydrogel compositions was thirty-four hundredthsof a millimeter (0.34 mm)±three hundredths of a millimeter (0.03 mm).

Example 2 Static and Kinetic Coefficients of Friction of the MembraneComposition

The static and kinetic coefficients of friction for twenty-four (24)preferred membrane compositions 5 were determined according to themethod provided in “ASTM D 1894-06 Standard Test Method for Static andKinetic Coefficients of Friction of Plastic Film and Sheeting.” Briefly,an Instron (model number 3342) with a one hundred Newton (100 N) loadcell was used to pull a one hundred thirty-nine and seven tenths grams(139.7 g) sled with the membrane composition 5 attached across a glasssurface at a rate of one hundred fifty millimeters per minute (150mm/min). The test was run at room temperature and moisture wasmaintained within the specimens throughout the test. See FIG. 2 for agraphical representation of the raw data. The static coefficient offriction was determined to be one hundred thirteen thousandths(0.113)±fifty-three thousandths (0.053). The kinetic coefficient offriction was determined to be one hundred three thousandths(0.103)±fifty-two thousandths (0.052).

Example 3 Suture Strength of the Membrane Compositions

The suture retention strength of a three tenths of a millimeter (0.3 mm)thick membrane composition and a three tenths of a millimeter (0.3 mm)thick hydrogel component 10 without filler were determined according toISO 7198 section 8.8 Determination of suture retention strength.Briefly, an Instron (model number 3342) with a 100N load cell was usedwith a simple tensile test grip apparatus. A 5-0 Prolene Suture withtaper point needle was passed two millimeters (2 mm) from the edge ofeach specimen and formed into a loop and fastened to the top grip of thetesting apparatus. The specimen was held with the bottom grip. TheInstron was then run at a rate of one hundred millimeters per minute(100 mm/min) until failure. The results of the test are shown in FIG. 3.The membrane composition (n=30) had a mean suture retention strength often and five hundredths Newtons (10.05 N)±one and forty-five hundredthsNewtons (1.45 N). The hydrogel component 10 alone specimens (n=3) had amean suture retention strength of twelve hundredths Newtons (0.12N)±twelve hundredths Newtons (0.12 N). As shown in this example, thematrix filler or base substrate provides a considerable effect withregard to suture retention strength.

Example 4 Tensile Properties of the Membrane Compositions

Tensile properties of the preferred membrane compositions 5 weredetermined in two different directions using an Instron (model number3342). Membrane compositions specimens with dimensions of approximatelyseventeen millimeters by thirty-eight millimeters by three tenths of amillimeter (17 mm×38 mm×0.30 mm) were created and cut according to thecomposite mesh knit directions. Six (6) specimens were then tested inthe direction of the courses on the fabric and another set of six (6)specimens were tested in the direction of the wales on the fabric. Afour hundredths Newton (0.04 N) preload was applied and the specimenswere tested at a rate of one hundred millimeters per minute (100mm/min). The data for both sets is presented in FIG. 4. The membranecompositions 5 were observed to be orthotropic, exhibiting significantlydifferent mechanical behaviors in the two directions evaluated. Further,the membrane compositions 5 exhibit nonlinear behavior and exponentialtype behavior with large displacements at very low loads followed by atensioning of the textile filler that leads to sharp increase in load atthe large extensions. This behavior is similar to soft tissues in thebody. These properties can be adjusted to match or mimic specific softtissue by adjustments in the hydrogel component 10 and textile component20 properties. This study demonstrated the ability of the membranecompositions 5 to stretch. The ability to stretch is valuable insurgical applications for handling purposes and to facilitate tensionfree repairs.

Example 5 Membrane Composition Flexibility

The flexibility of the preferred membrane compositions 5 was compared toan ePTFE sheet using a bending rigidity test apparatus according to ASTMD 5372-95 (Reapproved 2001) Stiffness of Nonwoven Fabrics Using theCantilever Test. Briefly, the method was a cantilever test in which aspecific length and width of the membrane composition 5 specimens wasevaluated for bending under its own weight. Bending length was measuredas a length of fabric that drapes over an edge and contacts a blade setat forty-one and one-half degrees (41.5°) from the horizontal. A totalof sixteen (16) membrane composition 5 specimens were tested and theaverage bend length was ten millimeters (10 mm)±four tenths of amillimeter (0.4 mm). The ePTFE sheet, a clinically approved device GorePreclude VesselGuarda with a similar thickness (0.3 mm), was measured inthe same test apparatus as a control and the average bend length wastwenty-two millimeters (22 mm)±one and four tenths millimeters (1.4 mm).The flexural rigidity of both membranes were calculated according to thestandard and determined to be thirty-four (0.34) g·m±four hundredths(0.04) g·m for the membrane composition and six and forty-fivehundredths (6.45) g·m±one and seventeen hundredths 1.17 g·m for theePTFE sheet (results are shown in FIG. 5). The results from this testexemplify the flexibility and pliability of the membrane composition 5that exhibits minimal flexural rigidity and resistance to bending ascompared to the ePTFE sheet. This feature of the membrane composition 5makes the membrane composition 5 ideal for lying interposed between softtissues and over metal plates or other implants or instruments. The lowstiffness and pliability give the material the ability to drape andcontour over other implants or critical structures.

Example 6 Surgical Setting Observations

A surgical setting was created using a human cadaver torso and anterioraccess instruments with multiple spine and spine access surgeons. Themembrane composition 5 was used in the cadaver labs as a cover andprotector over an anterior interbody fusion cage, anterior tension bandplate, and other anterior access spine procedures. The materialproperties of the preferred membrane composition 5 enabled it to contourto the spine and the surface of the metal implant, generally withoutbubbling. In addition, the surface tension of the water in the gelallowed the membrane composition 5 to temporarily stick to the surfacesin the body, the metal implants, and the metal instruments. This helpedprovide improved handling properties. Since the membrane composition 5of the preferred embodiment was translucent, it also assisted withplacement over the hardware and provided the surgeon visual feedback onthe location of important anatomical structures below the membrane 5.The membrane composition 5 contained several radiopaque markings thatwere visible under fluoroscopy. In addition, the membrane composition 5was fastened in place using tacks and sutures by the surgeons.

Example 7 Rat Model Studies

Membrane composition 5 samples of the preferred embodiment were preparedas described in Example 1 with the specified dimensions (1.5 cm×1.0cm×0.03 cm) and implanted in a rat cecal abrasion model. The desire ofthe study was to determine if the membrane composition 5 reduced theincidence and severity of adhesions. The study consisted of threegroups: 1) a control group with surgical trauma and no barrier (n=13);2) a clinically approved device Gore Preclude VesselGuard, which is anePTFE sheet, (n=10); and 3) the preferred membrane composition 5 (n=9).Within a seven day time window, ten of thirteen control animals formedadhesions. A mechanical test was performed to assess the tenacity ofthese adhesions. The energy absorbed at failure had a mean oftwenty-nine and one-half (29.5)±ten and four tenths millijoules (10.4mJ) and the mean peak load was one and three tenths (1.30)±one-halfNewton (0.50 N). Treatment with either the VesselGuard or the membranecomposition 5 barrier prevented adhesion formation between the abradedcecum and abdominal wall of the rat over the seven days. There were nostrong adhesions to the surface of the membrane composition 5 andhistology showed that the gel coating prevents or limits cells frommigrating into the mesh. Due to the complete absence of adhesions on thetwo barrier groups, mechanical testing could not be performed. A thinlayer cellular attachment was seen on both barriers evaluated. Histologyconfirmed a sub-acute to chronic inflammatory response due to thesurgical trauma and the absence of tissue in-growth into the preferredmembrane composition 5. (See FIG. 6A) Further, Congo red stain was usedto identify the hydrogel component 10 and in no case was there evidencethat the membrane composition 5 was delaminating or sheared. (See FIG.6B) In addition, the membrane composition suture fixation remainedattached throughout the implantation period. Finally, the VesselGuard isnot translucent as is the preferred membrane composition 5. Thetranslucency allows for greater visibility of the structures “behind”the membrane composition 5 once it has been positioned in a patient.

After the study, a histology image was used to determine the maximumpore size within the membrane composition gel matrix. Fifty maximumsized pores were measured digitally from a single three hundred forty byfour hundred twenty micrometer (340 μm×420 μm) histology image. The maxpore size within the representative area was measured to a mean size oftwo and seven tenths micrometers (2.7 μm)±nine tenths micrometers (0.9μm). It is preferred that the size of the pores is less than one hundredmicrometers (100 μm) to minimize cellular growth into the membranecomposition 5. One function of the hydrogel component 10 is to “fill in”the larger pores of the textile component 20 (as described above).

Example 8 Stability of the Membrane Compositions

Stability of the preferred membrane composition 5 was evaluatedaccording to the ISO 10993-13 Biological Evaluation of MedicalDevices—Identification and Quantification of Degradation Products fromPolymeric Medical Devices. Six (6) membrane compositions 5 were labeled1-6 (1-3 for controls and 4-6 for test samples) and dried overnight at aconstant temperature in a vacuum oven. All samples were weighed for drymass data. Samples 1-3 (controls) were analyzed with DifferentialScanning calorimetry (DSC) and Fourier transform spectroscopy (FT-IR)for pre-conditioning thermograms and spectra, while samples 4-6 (testsamples) were each put in a glass jar with forty milliliters (40 mL) ofdeionized (DI) water (following a ratio of one gram (1 g) ofsample:forty milliliters (40 mL) of DI water) for seven (7) days. DSCmeasures changes in heat flow. FT-IR measures chemical bond changes. Astable membrane composition 5 should not have changing bonds or heatflow (i.e., thermograms). Immediately after the immersion in DI water,samples 4-6 were put in a Binder oven set at fifty degrees Celsius (50°C.), monitored and recorded by a Fluke thermometer and thermocouple, forseven (7) days. At the end of seven (7) days, samples 4-6 were taken outof the oven, dried to a constant mass in a vacuum oven for a secondtime, and weighed for dry mass data. Samples 4-6 were then analyzed withDSC and FT-IR for post-conditioning thermograms and spectra. Theresidual DI water from the immersion of each implant was filtered(together with an extra ten milliliters (10 mL) rinse water for eachjar) using a Glass Microanalysis Filter Holder Assembly. The filterpapers were then dried to constant mass and weighed for residual drymass data. The FT-IR spectrum for samples 1-3 preconditioning and 4-6post-conditioning are shown in FIGS. 7A and 7B. Although some of thepeaks in FIG. 7B (the post-conditioning samples) are of greaterintensity than the same peaks in FIG. 7A (the pre-conditioning samples),there are no new peaks in the spectrums for the post-conditioningpreferred membrane compositions 5, which would be indicative ofdegrading polymers. The material balance and analysis showed that thepreferred membrane composition 5 was stable and did not break down ordissolve during stability testing. This verified the permanent nature ofthe membrane composition 5.

The embodiments set forth above, among those made apparent from thepreceding description, are efficiently attained and, since certainchanges may be made in carrying out the above method of forming and inthe resulting composition without departing from the spirit and scope ofthe invention, it is intended that all material contained in the abovedescription shall be interpreted as illustrative and not in a limitingsense.

It will also be understood that the embodiments presented herein areintended to cover all of the generic and specific features of thecomposition barrier herein described and all statements of the scope ofthe invention which, as a matter of language, might be said to falltherebetween. Particularly it is to be understood that in saidembodiments, ingredients or compounds recited in the singular areintended to include compatible mixtures of such ingredients.

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular embodiments disclosed, but isintended to cover modifications within the spirit and scope of thepresent invention as defined by the appended claims.

The invention claimed is:
 1. A membrane for securement to a patient'sbone or soft tissue to reduce the formation of tissue adhesionsfollowing a surgical procedure comprising a hydrogel includingpoly(vinyl alcohol) crosslinked to a second polymer, wherein a ratio ofthe poly(vinyl alcohol) to the second polymer ranges from about 75:1 toabout 200:1, wherein the membrane has a static coefficient of frictionbetween about one hundredth (0.01) and about one-half (0.5), a kineticcoefficient of friction between about one hundredth (0.01) and aboutone-half (0.5), and flexibility of less than thirty millimeters (30 mm)bend length, and wherein the membrane is formed into a single, planarsheet.
 2. The membrane of claim 1, wherein the second polymer isselected from the group consisting of poly(vinyl pyrrolidone),poly(hydroxyethylmethacrylate), poly(acrylamide), poly(acrylic acid),poly(acrylonitrile), polyethylene imine and poly(ethylene glycol). 3.The membrane of claim 1, wherein the second polymer is poly(vinylpyrrolidone).
 4. The membrane of claim 1, wherein the ratio ranges fromabout 75:1 to about 110:1.
 5. The membrane of claim 1, wherein thepoly(vinyl alcohol) and the second polymer are crosslinked by a methodselected from the group consisting of cryogelation, dehydrationprocessing, radiation and exposure to chemicals.
 6. The membrane ofclaim 1, wherein the membrane has a thickness between about two tenthsof a millimeter (0.2 mm) to about three millimeters (3 mm).
 7. Themembrane of claim 1, wherein the membrane has a thickness between aboutthree tenths of a millimeter (0.3 mm) to about one and one-halfmillimeters (1.5 mm).
 8. The membrane of claim 1, further comprisingradiopaque markings.
 9. A membrane composition for securement to apatient's bone or tissue comprising a hydrogel including poly(vinylalcohol) and a second polymer selected from the group consisting ofpoly(vinyl pyrrolidone), poly(hydroxyethylmethacrylate),poly(acrylamide), poly(acrylic acid), poly(acrylonitrile), polyethyleneimine and poly(ethylene glycol), wherein the poly(vinyl alcohol) and thesecond polymer are crosslinked and a ratio of the poly(vinyl alcohol) tothe second polymer ranges from about 75:1 to about 200:1, wherein thecomposition has sufficient thickness, lubricity and flexibility toreduce the formation of tissue adhesions following a surgical procedure,and wherein the composition is formed into a single, planar sheetconfigured to adhere to the patient's spine to provide a plane ofdissection between the spine and tissue.
 10. The composition of claim 9,wherein the second polymer is poly(vinyl pyrrolidone).
 11. Thecomposition of claim 9, wherein the ratio ranges from about 75:1 toabout 110:1.
 12. The composition of claim 9, wherein the poly(vinylalcohol) and the second polymer are crosslinked by a method selectedfrom the group consisting of cryogelation, dehydration processing,radiation and exposure to chemicals.
 13. The composition of claim 9,wherein the composition has a thickness between about two tenths of amillimeter (0.2 mm) to about three millimeters (3 mm).
 14. Thecomposition of claim 9, wherein the composition has a thickness betweenabout three tenths of a millimeter (03 mm) to about one and one-halfmillimeters (1.5 mm).
 15. The composition of claim 9, further comprisingradiopaque markings.
 16. The composition of claim 9, wherein thecomposition has a water content between about fifty percent (50%) andabout eighty-five percent (85%).
 17. A membrane for use as a surgicalimplant comprising: a hydrogel including poly(vinyl alcohol) andpoly(vinyl pyrrolidone), wherein a ratio of the poly(vinyl alcohol) tothe poly(vinyl pyrrolidone) is between about 75:1 and about 200:1,wherein the membrane has a thickness between about three tenths of amillimeter (0.3 mm) and about one and one-half millimeters (1.5 mm),wherein the poly(vinyl alcohol) and the poly(vinyl pyrrolidone) arecrosslinked by cryogelation, wherein the membrane has a water contentbetween about sixty-eight percent (68%) and about seventy-five percent(75%).
 18. The membrane of claim 17, wherein the ratio is between about75:1 and about 110:1.